Method for producing electrical steel core laminations

ABSTRACT

Core laminations are stamped from electrical steel strip and stress annealed by induction heating in a closed tubular chute inclined downwardly from the stamping press. A preselected, non-ambient atmosphere is maintained within the chute.

BACKGROUND OF THE INVENTION

The present invention relates generally to the production of electricalsteel core laminations and more particularly to a method and apparatusfor doing so.

Electrical steel core laminations are used in the cores of rotors andstators for electric motors and in the cores of small transformers, forexample. These laminations are stamped by a manufacturer thereof fromcold rolled steel strip which is usually subjected to a decarburizinganneal either before the stamping operation, by the steel maker, orafter the stamping operation, by the manufacturer of the laminations.The considerations involved in the composition and processing of thecold rolled steel strip before stamping, in the decarburization thereofand in the stamping, annealing and other operations performed by eitherthe steel maker or the manufacturer of the laminations, are discussed insome detail in Rastogi U.S. Pat. No. 4,390,378 and in Rastogi, et al.U.S. Pat. No. 4,601,766, and the disclosures of both of these patentsare incorporated herein by reference.

It is usually more desirable for the decarburizing anneal to beperformed by the steel maker rather than by the lamination manufacturer.In those situations where the manufacturer of the lamination does notperform a decarburizing anneal after stamping the lamination, anothertype of anneal is usually performed to relieve the stresses resultingfrom the stamping operation and to enhance the magnetic properties ofthe lamination.

All anneals performed by the manufacturer of the lamination, whether adecarburizing anneal or a stress relieving anneal, are usually conductedat a location remote from the stamping press at which the lamination wasmade. Typically, the lamination is conducted away from the stampingpress through a downwardly inclined chute having an upper, entry endlocated adjacent the stamping press to receive a lamination after it hasbeen stamped on the press. The chute is typically trough-shaped, open atthe top, and the chute communicates at its lower, exit end with aconveyor or other material handling device for transporting thelaminations from the exit end of the chute to an annealing furnace. Thelaminations move through the downwardly inclined chute at leastpartially under the urging of gravity.

The annealing furnace may be gas fired, for example, or an inductionfurnace may be employed.

Koshiishi, et al. U.S. Pat. No. 4,602,969 discloses a method forsubjecting core blanks (laminations) to a stress relieving anneal afterthe core blanks have undergone blanking, presumably at a stamping press.The core blanks are transported by a conveyor, presumably from thestamping press, to annealing equipment wherein the core blanks areinitially elevated upwardly through a vertical tube containing inductionheating coils. At the top of the induction heating tube, the core blanksare discharged onto another conveyor which transports the core blanksthrough a soaking heating chamber followed by a cooling chamber. InKoshiishi, et al. the core blanks are annealed after they have beenconveyed away from the stamping press to an annealing furnace remotefrom the press, and complicated apparatuses are employed to elevate thestamped laminations through the vertically disposed induction heatingarrangement, and then to convey the core blanks through additional heattreating equipment. The core blanks are subjected to loading andunloading operations at an annealing furnace, as well as other materialhandling operations, separate and discrete from those employed toconduct the core blanks away from the stamping press.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus forsubjecting a stamped core lamination to a stress relief anneal underconditions which minimize loading, unloading and other handling of thestamped laminations and shorten the annealing time.

In accordance with the present invention, the downwardly inclined chutethrough which the laminations are conducted away from the stamping presshas a tubular cross section so as to totally enclose the laminations inthe chute. The stress relief anneal is performed by induction heatingthe laminations in the chute, as the laminations are conducted away fromthe stamping press. The laminations in the chute are maintained intightly packed, face to face, abutting relation without intentionalspacing between adjacent laminations, during the totality of the timethe laminations are undergoing induction heating. Preferably anon-oxidizing atmosphere is maintained within the chute. The time,temperature and atmospheric conditions employed in connection with theannealing operation are such that the steel strip may be coated with aninorganic coating or a combination of inorganic and organic coatingsprior to the stamping step, and those coatings are not adverselyeffected during the annealing operation.

The upper, inlet end of the downwardly inclined chute is locatedadjacent the stamping press and receives laminations directly from thestamping press, without any intermediate conveyance. Laminationswithdrawn from the lower, exit end of the downwardly inclined chutehave, by then, been subjected to the desired stress relief anneal andmay be used in a motor or transformer core without further heattreatment. Conveying the laminations to an annealing furnace at alocation remote from the stamping press, and loading and unloading thelaminations into and out of the remote annealing furnace are eliminated.

The annealing furnace itself, and the apparatus for conducting thelaminations through the annealing furnace are relatively uncomplicated.

Other features and advantages are inherent in the method and apparatusclaimed and disclosed or will become apparent to those skilled in theart from the following detailed description in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram, in side elevation, illustrating anembodiment of a method and apparatus for manufacturing electrical steellaminations in accordance with the present invention;

FIG. 2 is an enlarged, sectional view taken along line 2--2 in FIG. 1;

FIG. 3 is an enlarged, fragmentary, sectional view of a portion of theapparatus illustrated in FIG. 1; and

FIG. 4 is an enlarged, fragmentary view of another portion of theapparatus illustrated in FIG. 1.

DETAILED DESCRIPTION

Referring initially to FIG. 1, indicated generally at 10 is a stampingpress comprising a lower stationary part or fixed die 11 and an upper,vertically movable part 12 for stamping a lamination 14 from electricalsteel strip. Stamping press 10 is of conventional construction.

A downwardly inclined, tubular chute 15 has an upper, entry end 16located adjacent stamping press 10. Entry end 16 comprises means forreceiving a lamination 14 stamped at press 10. Lamination 14 isdelivered from press 10 to the adjacent upper entry end 16 of chute 15in a conventional manner employing conventional devices heretoforeemployed to deliver laminations from a stamping press to thetrough-shaped chute conventionally employed with such stamping presses.

In another embodiment, the fixed die 11 is located higher than thechute's entry end 16, and the stamped lamination drops through thebottom of fixed die 11 and is guided, in a conventional manner, to thechute's entry end 16.

Chute 15 extends in a downwardly inclined direction from upper entry end16 to an exit end 17 which is lower than entry end 16. The angle ofinclination of chute 15 is typically downward at 45°. Downwardlyinclined chute 15 comprises structure for conducting laminations awayfrom stamping press 10. Because of its closed, tubular construction(FIGS. 1 and 2) chute 15 totally encloses laminations 14.

Located around at least a portion of the length of tubular chute 15 isan induction heating coil 18, for annealing laminations 14 conductedaway from stamping press 10 by chute 15. Opposite ends of coil 18 areelectrically coupled to a power source (not shown) in a conventionalmanner. In the embodiment shown in FIG. 1, induction heating coil 18extends from an upper, terminal position 19 adjacent entry end 16 ofchute 15, to a lower terminal position 20 at an intermediate location onthe chute, lower than chute entry end 16 and higher than chute exit end17.

Chute 15 is tubular and closed along at least that portion of the chutearound which induction heating coil 18 is located. Chute 15 can betubular and closed along its entire length, although it need not be wheninduction heating coil 18 does not encircle tube 15 for the tube'sentire length.

As shown in FIGS. 1 and 3, laminations 14 in chute 15 are maintained ina tightly packed, face to face, abutting relation without intentionalspacing between the laminations along at least that portion of the chutearound which induction heating coil 18 is located.

Located adjacent chute exit end 17 is a conveyor 25 for receiving andconveying away from chute 15 laminations 14 which exit from chute exitend 17.

When chute 15 is empty, at the beginning of a stamping operation, thereis located within chute 15, at upper entry end 16, a steel dummy bar 26attached to an arm 27 (FIG. 4). The first lamination 14 introduced intochute 15 through upper entry end 16 abuts against dummy bar 26, and asadditional laminations 14 are received within chute 15 through upperentry end 16, dummy bar 26 is withdrawn, incrementally, downwardlythrough chute 15, by a pulling action exerted on arm 27. Eventually,dummy bar 26 is withdrawn entirely from chute 15, at which time chute 15is filled with tightly packed, face to face, abutting laminations 14,i.e. a continuum of individual laminations. Dummy bar 26 maintains thelaminations in that relationship from the time the first two laminationshave been received within chute 15, until the dummy bar is withdrawnfrom chute 15 through exit end 17.

In addition to working on a continuum of individual laminations 14, theannealing step can be employed on a continuum of bundles 29, (FIG. 1),each assembled from a sub-continuum comprising a number of laminations14 equal to the number in a rotor or stator. Bundles 29 are assembledprior to being received within chute 15 at upper entry end 16. All ofthe laminations 14 within a bundle 29 are in tightly packed, face toface, abutting relation, and all of the bundles 29 in chute 15 are intightly packed, face to face, abutting relation with each other.Conveyor 25 conducts away from chute 15 bundles 29 exiting chute 15 atexit end 17 (dash-dot lines in FIG. 1).

At the beginning of an annealing operation, one or more bundles 29 maybe employed in lieu of dummy bar 26 (FIG. 4), and those bundles performthe same function as the dummy bar. Steel dummy bar 26, or one or morebundles 29 employed in lieu of a dummy bar, preferably should extend thefull length of induction heating coil 18, from position 19 to position20 (FIG. 1), as this will permit an immediate start of the inductionheating operation once the first lamination 14 is received at chuteentry end 16.

When bundles 29 are employed, upper terminal position 19 of coil 18 isspaced from chute entry end 16 a distance equal to or greater than thedimension of a bundle in the lengthwise direction of chute 15. Thisspacing accommodates the time delay between the introduction of twoadjacent bundles 29 at chute entry end 16 and permits the maintenance ofa continuum of bundles 29 between the coil's two terminal positions 19and 20.

Associated with chute 15 is a gas inlet 22 positioned on chute 15 at afirst location thereon relatively remote from chute entry end 16. Alsoassociated with chute 15 is a gas outlet 23 positioned on chute 15 at asecond location thereon higher than the location of gas inlet 22 andcloser to chute entry end 16. Gas inlet 22 is employed for introducing agaseous medium into chute 15, and gas outlet 23 is employed forwithdrawing from chute 15 the gaseous medium introduced at gas inlet 22.The gaseous medium is employed to maintain a preselected, non-ambientatmosphere within chute 15 between gas inlet 22 and gas outlet 23.

Gas outlet 23 is preferably located on chute 15 no lower than upperterminal position 19 of coil 18, and gas inlet 22 is preferably locatedon chute 15 no higher than lower terminal position 20 of coil 18.Positioning the gas inlet and outlet, thusly, assures that laminations14 are subjected to the desired atmosphere during the totality of thetime the laminations are subjected to induction heating by coil 18.

The cold rolled steel strip from which laminations 14 are stamped haspreviously been decarburized to the extent desired, before the stampingoperation, and the annealing operation conducted in chute 15 is anon-decarburizing anneal. Accordingly the gaseous atmosphere maintainedwithin chute 15 is non-decarburizing and usually non-oxidizing.

Steels which have been fully decarburized, e.g. to a carbon content of0.007 wt. % or less, are oftentimes referred to as fully processed orfull hard electrical steels. Steels which have not been fullydecarburized are referred to as semi-processed steels. The method andapparatus of the present invention can be employed on both fullyprocessed steels and semi-processed steels, but on the latter only inthose situations where relatively high magnetic properties are notnecessary.

In the preferred embodiment illustrated in FIG. 1, the annealing step isinitiated at 19, adjacent upstream end 16 of chute 15 and terminated atintermediate location 20 downstream of where the annealing step wasinitiated and upstream of downstream end 17 of chute 15. As noted above,laminations 14 are totally enclosed within closed tubular chute 15 forat least the time during which they are subjected to the annealing step.

The laminations are cooled between intermediate location 20 anddownstream chute end 17. The annealing operation is typically conductedat a temperature in the range 900°-1500° F. (482°-816° C.) for a timeperiod in the range 1-5 minutes. Laminations 14 normally spend a periodof time in chute 15 longer than the time required for a stress reliefanneal. For example, a typical chute 15 is 10 ft. (305 cm.) long, andthe laminations move through the chute at the rate of about 4 inches (10cm.) per minute. Under those conditions, the laminations spend about 30minutes in the chute. A heating coil which surrounded chute 15 for about20 inches (51 cm.) along the chute's length would produce a heatingperiod of about 5 minutes. If the laminations were induction heatedalong the upper 20 inches of chute 15, they would then undergo coolingfor the remainder of the time they spent in the chute, e.g. 25 minutesof cooling.

The annealing operation can be completed in a relatively short period oftime because of the rapidity with which the laminations are heated byinduction heating. However, induction heating is useful only if theparts subjected thereto are tightly packed for the entirety of thatportion of the length of chute 15 which is surrounded by inductionheating coil 18. In other words, coil 18 must surround a continuum oflaminations 14 within chute 15 in order to accomplish induction heating.

As noted above, during the annealing operation the laminations aresubjected to a preselected, non-ambient atmosphere which is typicallynon-oxidizing, e.g. an inert gas such as dry nitrogen or argon or areducing gas such as a hydrogen-nitrogen mixture. It is desirable toavoid an ambient atmosphere within chute 15, thereby avoiding theformation of a flaky oxide on laminations 14. In addition to the gaseousatmospheres described above, one may alternatively employ a wet nitrogenatmosphere to apply a protective coating on laminations 14, a so-calledbluing operation. The wet nitrogen atmosphere would have a conventionalcomposition heretofore used for bluing purposes.

When the atmosphere within chute 15 is non-ambient and non-oxidizing,the steel strip from which the laminations are stamped may be coated,prior to the stamping step, with an inorganic coating or a combinationinorganic-organic coating, and that coating will not be adverselyeffected during the annealing of the laminations in chute 15 because ofthe provision within chute 15 of a non-oxidizing, gaseous atmosphere.The coating applied to the steel strip, before stamping, may be one ofseveral conventional coatings which have heretofore been applied tofully processed cold rolled steel strip, before the strip was subjectedto a stamping operation to produce laminations, e.g. phosphate orchromate coatings. Inorganic or combination inorganic-organic coatingscan withstand the temperature to which the laminations are subjectedduring a stress relief anneal in accordance with the present invention.A pure organic coating cannot be used because it would decompose at thattemperature.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications will be obvious to those skilled in the art.

I claim:
 1. In a method for manufacturing core laminations fromelectrical steel strip which has been decarburized to the extentdesired, and wherein (a) core laminations are stamped from said strip ata stamping press, (b) said laminations are conducted away from saidpress in a downwardly inclined chute located adjacent said press, and(c) the laminations are then annealed without decarburization, theimprovement comprising the steps of:totally enclosing the laminations insaid chute; performing said annealing step by induction heating thelaminations in said chute, as the laminations are conducted away fromsaid press; and maintaining said laminations in said chute in tightlypacked, face to face, abutting relation without intentional spacingbetween adjacent laminations, during the totality of the time thelaminations are undergoing induction heating.
 2. In a method as recitedin claim 1 wherein said chute has an upstream end and a downstream end,said method comprising:initiating said annealing step at an upperterminal position adjacent said upstream end of the chute.
 3. In amethod as recited in claim 2 and comprising:terminating said annealingstep at a lower terminal position constituting an intermediate locationon said chute downstream of where said annealing step was initiated andupstream of said downstream end of the chute; and cooling said annealedlaminations between said intermediate location and the downstream end ofthe chute as said laminations move downstream from said intermediatelocation.
 4. In a method as recited in claim 1 wherein said chute has anupstream end and a downstream end, said method comprising:introducing agaseous medium into said chute at a first location relatively remotefrom said upstream end of the chute; withdrawing said gaseous mediumfrom the chute at a second location upstream of said first location; andemploying said gaseous medium to maintain a non-ambient atmospherewithin said chute between said first and second locations.
 5. In amethod as recited in claim 4 wherein said atmosphere is non-oxidizing.6. In a method as recited in claim 4 wherein said atmosphere is selectedfrom the group consisting of wet nitrogen, dry nitrogen, ahydrogen-nitrogen mixture and argon.
 7. In the method of claim 4 andcomprising:initiating said annealing step at an upper terminal positionadjacent said upstream end of the chute; terminating said annealing stepat a lower terminal position constituting an intermediate location onsaid chute downstream of where said annealing step was initiated andupstream of said downstream end of the chute; said location on the chutewhere said gaseous medium is withdrawn being no lower than said upperterminal position where said annealing step is initiated; and saidlocation on the chute where said gaseous medium is introduced being nohigher than said lower terminal position where said annealing step isterminated.
 8. In a method as recited in claim 1 wherein:each laminationis induction heated in said chute at a temperature in the range of about900°-1500° F. (482°-816° C.) for a time in the range of about 1-5minutes.
 9. In a method as recited in claim 1 and comprising:coatingsaid steel strip with an inorganic coating or a combinationinorganic-organic coating prior to stamping core limitations from saidstrip; and providing said chute with a non-oxidizing, gaseous atmosphereduring said annealing step.
 10. In a method as recited in claim 1wherein:said laminations are totally enclosed for at least the timeduring which the annealing step is being performed.